Composite grid wire for electron tubes



United States Patent 3 323 882 COlWPOSlTE GRID WIRE FOR ELECTRON TUBESHenry J. Albert, Colts Neck, NJ., assignor to Engelhard Industries,Inc., Newark, N.J., a corporation of Delaware No Drawing. Filed Dec. 6,1966, Ser. No. 599,364 3 Claims. (Cl. 29-193) ABSTRACT OF THE DISCLOSUREThe present invention deals with a composite emission inhibiting gridwire for electron tubes which resists embrittlement at high operatingtemperatures, which has high tensile strength and maintains a resistanceagainst grain-growth and creep at elevated temperatures, and which iscomposed of a core of interfused wires of a 50/50 molybdenum-rheniumalloy with the core being coated with titanium.

Background of the invention In electron tubes employing hot electronemissive cathodes of the activated type, e.g. thoriated cathodes, inconjunction with grids of a refractory material, e.g. tungsten, tantalumand molybdenum, which must be essentially free of activation material,it has been found that the grids suffer from contamination by theactivation material and lose stability unless protected by an electronemission inhibiting material. Generally, the grids are coated with anelectron emission inhibiting material comprising a coating of platinum,gold or titanium.

Such coated grids, while effectively inhibiting electron emission, havea tendency to become embrittled when employed for long periods at theelevated operating temperatures of the tubes, the embrittlement beingcaused by the grain-growth of the grid metal with a consequent shortstress-rupture time which limits the useful life of the grid.

Summary of the invention In accordance with the invention, it has beenfound that a grid wire having a core composed of about 50/50molybdenum-rhenium alloy with the core being coated with a layer oftitanium provides an effective emission inhibiting grid structure whichis characterized by high tensile strength and resistance againstbreakage by creep and grain-growth at elevated temperatures when thecore metal is in a fibrous form of interfused wires.

Description of the preferred embodiments In providing the composite gridwire of the invention, a substantially heavy-walled titanium tube isprepared. For example, the tube may have a wall thickness of about0.065" with an OD. of about 0.540" and a length of about 6.0".

Also, a suitable length of wire having a diameter of about 0.20 andcomposed of about 50/50 molybdenumrhenium alloy is provided. The termabout 50/50 molybdenum-rhenium alloy includes an alloy composition of48%-52% molybdenum and 52%-48% rhenium by weight percent. The wire iscut into lengths of about ice 6.0" to substantially correspond with thelength of the titanium tube. Both the titanium tube and themolybdenum-rhenium wires are thoroughly cleaned by known procedure toremove surface contaminants. Between about to about 200 of the wires areinserted into the titanium tube and the composite rod is reduced by coldswaging initially to about 50% reduction which is possible due to theelimination of the voids between the wires. Thereafter, the compositerod is reduced to wire by alternately annealing and cold drawing withthe average reduction between anneals ranging from about 25% to about37.5% reduction. The annealing is accomplished by heating the compositein vacuum at about 1000 C., for example, between about 1200 C. to 1600C. for from 2 to 3 hours, and the wire is thusly drawn to about 0.032diameter. During the Working of the composite wire, the core wiresbecame interfused into a mass having a fibrous grain structure such thatthe fibrous grains are elongated along the length of the core and thecore is bonded directly to the coating layer.

The mechanical properties of the resultant composite Wire is shown inthe following table:

-It will be seen that the elongation of the composite wire issubstantially constant in both the cold worked and annealed condition,which is a result of the core composed of the fibrous interfused wires.

When the composite wire of the invention is employed as a grid inelectron tubes operating at high temperatures, there is practically noembrittlement of the grid because the transformation of the plurality ofcore wires by interfusion into a fibrous mass of elongated grainsresists embrittlement at high operating temperatures by inhibitinggrain-growth of the core grains.

Consequently, the composite grid wire of the invention is characterizedby a long useful life during operation of the electron tubes.

What is claimed is:

1. A composite emission inhibiting gn'd wire for electron tubes,comprising a core in the form of a mass of interfused wires in fibrousform composed of an alloy of 48% to 52% molybdenum and 52% to 48%rhenium, and a coating of titanium bonded directly to the core.

2. A composite grid wire according to claim 1, wherein the core iscomposed of a 50/50 molybdenum rhenium alloy.

3. A composite grid wire according to claim 1, wherein the compositewire is characterized by a substantially constant elongation both in thecold-worked and annealed conditions.

No references cited.

HYLAND BIZOT, Primary Examiner.

1. A COMPOSITE EMISSION INHIBITING GRID WIRE FOR ELECTRON TUBES,COMPRISING A CORE IN THE FORM OF A MASS OF INTERFUSED WIRES IN FIBROUSFORM COMPOSED OF AN ALLOY OF 48% TO 52% MOLYBDENUM AND 52% TO 48%RHENIUM, AND A COATING OF TITANIUM BONDED DIRECTLY TO THE CORE.